Image sensor using a boosting capacitor and a negative bias voltage

Abstract

An image sensor includes a photodiode generating a charge in response to light, a transfer transistor connecting the photodiode and a floating diffusion, a reset transistor connected between the floating diffusion and a power node, a boosting capacitor connected to the floating diffusion, and adjusting a capacity of the floating diffusion in response to a boosting control signal, and a bias circuit having first and second current circuits for supplying different bias currents to an output node to which a voltage signal corresponding to a charge accumulated in the floating diffusion is output. The boosting control signal decreases from a high level to a low level after the transfer transistor is turned off, and the reset transistor is switched from a turned on state to a turned off state when the bias currents of the first and second current circuits are simultaneously provided to the output node.

What is claimed is: 
     
       1. An image sensor, comprising:
 a row driver; 
 a photodiode connected to a first power node configured to supply a first source voltage, and configured to generate a charge in response to light; 
 a transfer transistor connecting the photodiode and a floating diffusion in response to a transmission control signal; 
 a reset transistor connected between the floating diffusion and a second power node configured to supply a second source voltage that is higher than the first source voltage; 
 a boosting capacitor connected directly to the floating diffusion and a control node where a boosting control signal is input, and configured to adjust a capacity of the floating diffusion in response to the boosting control signal; and 
 a bias circuit having a first current circuit and a second current circuit configured to supply different bias currents to an output node to which a voltage signal corresponding to a charge accumulated in the floating diffusion is output, 
 wherein the control node is different from the first power node, 
 wherein the first current circuit and the second current circuit are configured to simultaneously provide a first bias current and a second bias current to the output node during a first time, respectively, 
 wherein the row driver is configured to:
 decrease the boosting control signal from a high level to a low level after turning off the transfer transistor; and 
 switch the reset transistor from a turned on state to a turned off state during the first time, 
 
 wherein the second current circuit is further configured to provide the second bias current to the output node during a second time, 
 wherein the row driver is further configured to switch the transfer transistor from a turned on state to a turned off state during the second time, and 
 wherein the second time is different from the first time. 
 
     
     
       2. The image sensor of  claim 1 , wherein the row driver is further configured to increase the boosting control signal from a low level to a high level before turning on the transfer transistor. 
     
     
       3. The image sensor of  claim 1 , wherein the row driver is further configured to increase the boosting control signal from a low level to a high level after turning off the transfer transistor. 
     
     
       4. The image sensor of  claim 1 , further comprising a selection transistor connected between the output node and the floating diffusion, wherein:
 the selection transistor is configured to output the voltage signal corresponding to the charge accumulated in the floating diffusion to the output node; and 
 the first current circuit is further configured to provide the first bias current while the selection transistor is in a turned off state. 
 
     
     
       5. The image sensor of  claim 1 , wherein the row driver is further configured to increase the boosting control signal from a low level to a high level after turning off the reset transistor. 
     
     
       6. The image sensor of  claim 5 , wherein the row driver is further configured to turn on the reset transistor after decreasing the boosting control signal from a high level to a low level. 
     
     
       7. An image sensor, comprising:
 a row driver; 
 a first semiconductor chip that includes:
 a photodiode configured to generate a charge in response to light and connected to a floating diffusion and a first power node configured to supply a first source voltage to the photodiode, 
 a reset transistor connected between the floating diffusion and a second power node configured to supply a second source voltage, 
 a transfer transistor configured to transfer the charge generated by the photodiode to the floating diffusion, 
 a boosting capacitor connected directly to the floating diffusion and a control node where a boosting control signal is input, and configured to adjust a capacity of the floating diffusion in response to the boosting control signal, and 
 an output node configured to output a voltage signal corresponding to a charge accumulated in the floating diffusion; and 
 
 a second semiconductor chip connected to the output node through a metal pad and including a first current circuit and a second current circuit, 
 wherein the first current circuit and the second current circuit are configured to simultaneously provide a first bias current and a second bias current to the output node during a first time, respectively, 
 wherein the second source voltage is higher than the first source voltage, and 
 wherein the row driver is configured to:
 decrease the boosting control signal from a high level to a low level after turning off the transfer transistor; 
 switch the reset transistor from a turned-on state to a turned-off state during the first time; and 
 switch the transfer transistor from a turned-on state to a turned-off state during a second time different from the first time. 
 
 
     
     
       8. The image sensor of  claim 7 , wherein the row driver is further configured to increase the boosting control signal from a low level to a high level before turning off the transfer transistor. 
     
     
       9. The image sensor of  claim 7 , wherein the row driver is further configured to increase the boosting control signal from a low level to a high level after turning on the transfer transistor. 
     
     
       10. The image sensor of  claim 7 , wherein the first semiconductor chip further comprises:
 a source follower transistor configured to generate the voltage signal corresponding to the charge accumulated in the floating diffusion; and 
 a selection transistor configured to transfer the voltage signal to the output node in response to a selection control signal.